For the hundreds of years that sail power has been used to propel boats, there has always been a need for access to the top of the masts which support the sails. The sailing, rigging and supporting structures frequently require maintenance and repairs, sometimes in critical circumstances, such as during bad weather or while racing. However, the limited space available around the mast and rigging has precluded use of conventional devices such as ladders and the danger involved in ascending to a precarious position atop a tall mast requires safety considerations which compound the problem.
Traditional means of access to the top of boat masts has included permanent rope ladders as a part of the rigging, or a chair or sling attached to a pulley at the top of the mast. The ladder devices are known as bosun's chairs and are widely used because they can use existing rigging which is otherwise used to haul up the sails. The danger involved in use of a bosun's chair however, limits its use during underway condition, and is time consuming in any conditions.
Other devices have appeared in the art such as fixed steps on the mast and extending devices that must be hoisted up the mast. The disadvantage of fixed devices is that their protrusions interfere with the operation of the rigging and with the airflow around the mast. Airflow disturbances can be critical and aerodynamic qualities of the mast shape itself are important in racing design.